Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $88.62   8.625%   $96.2635   $96.26   $96.25   $96.30  
  Purchase #2 $213.79   3.540%   $221.3582   $221.36   $221.35   $221.40  
  Purchase #3 $106.83   5.847%   $113.0764   $113.08   $113.10   $113.10  
  Purchase #4 $182.40   7.585%   $196.235   $196.24   $196.25   $196.20  
  Purchase #5 $48.26   6.576%   $51.4336   $51.43   $51.45   $51.40  
  Purchase #6 $35.44   3.499%   $36.68   $36.68   $36.70   $36.70  
  Purchase #7 $231.99   9.287%   $253.5349   $253.53   $253.55   $253.50  
  7 purchase totals = $907.33       $968.5816   $968.58   $968.65   $968.60